U.S. patent application number 10/894305 was filed with the patent office on 2008-06-12 for preparation of cathode active material by hydrothermal reaction.
Invention is credited to Veronica Lamothe, Randolph Leising, Esther S. Takeuchi.
Application Number | 20080138707 10/894305 |
Document ID | / |
Family ID | 39498469 |
Filed Date | 2008-06-12 |
United States Patent
Application |
20080138707 |
Kind Code |
A1 |
Takeuchi; Esther S. ; et
al. |
June 12, 2008 |
Preparation of cathode active material by hydrothermal reaction
Abstract
The current invention relates to the preparation of an improved
cathode active material for non-aqueous lithium electrochemical
cell. In particular, the cathode active material comprised
.epsilon.-phase silver vanadium oxide prepared by using silver- and
vanadium-containing starting materials in a stoichiometric molar
proportion to give a Ag:V ratio of about 1:2. The reactants are
homogenized and then added to an aqueous solution followed by
heating in a pressurized vessel. The resulting .epsilon.-phase SVO
possesses a higher surface area than .epsilon.-phase SVO produced
by other prior art techniques. Consequently, the .epsilon.-phase
SVO material provides an advantage in greater discharge capacity in
pulse dischargeable cells.
Inventors: |
Takeuchi; Esther S.; (East
Amherst, NY) ; Lamothe; Veronica; (Lancaster, NY)
; Leising; Randolph; (Williamsville, NY) |
Correspondence
Address: |
Greatbatch Ltd.
10,000 Wehrle Drive
Clarence
NY
14031
US
|
Family ID: |
39498469 |
Appl. No.: |
10/894305 |
Filed: |
July 19, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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60488271 |
Jul 18, 2003 |
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Current U.S.
Class: |
429/219 ;
423/594.8; 423/604; 429/231.5 |
Current CPC
Class: |
C01P 2004/03 20130101;
B82Y 30/00 20130101; H01M 4/131 20130101; H01M 4/1391 20130101;
Y02E 60/10 20130101; C01G 31/006 20130101; C01G 31/00 20130101;
H01M 4/54 20130101; C01P 2006/12 20130101; H01M 4/505 20130101;
C01P 2006/40 20130101; C01G 31/02 20130101; C01P 2004/64
20130101 |
Class at
Publication: |
429/219 ;
429/231.5; 423/594.8; 423/604 |
International
Class: |
H01M 4/54 20060101
H01M004/54; C01G 31/02 20060101 C01G031/02; C01G 5/00 20060101
C01G005/00 |
Claims
1. An electrode active material comprising silver vanadium oxide
characterized as prepared by mixing a silver-containing material
and a vanadium-containing material in a solution contained in a
closed vessel heated to a reaction temperature above ambient of not
greater than about 300.degree. C.
2. The electrode of claim 1 wherein the silver vanadium oxide has
the formula Ag.sub.2V.sub.4O.sub.11.
3. The electrode active material of claim 1 wherein the reaction
temperature inside the closed vessel is from about 120.degree. C.
to about 300.degree. C.
4. The electrode active material of claim 1 wherein the pressure in
the closed vessel at the reaction temperature is about 14.7 psi to
about 1,800 psi.
5. The electrode active material of claim 1 wherein the solution
inside the closed vessel is characterized as having been heated at
the reaction temperature for about 1 hour to about 30 hours.
6. The electrode active material of claim 1 wherein the silver- and
vanadium-containing materials are in an aqueous solution in the
closed vessel in a stoichiometric molar proportion to give a Ag:V
ratio of about 1:2.
7. The electrode active material of claim 1 wherein the
silver-containing material is selected from the group consisting of
elemental silver, silver oxide, silver carbonate, silver lactate,
silver triflate, silver pentafluoropropionate, silver laurate,
silver myristate, silver palmitate, silver stearate, silver
vanadate, and mixtures thereof, and wherein the vanadium-containing
material is selected from the group consisting of NH.sub.4VO.sub.3,
AgVO.sub.3, VO, VO.sub.1.27, VO.sub.2, V.sub.2O.sub.4,
V.sub.2O.sub.3, V.sub.3O.sub.5, V.sub.4O.sub.9, V.sub.6O.sub.13,
V.sub.2O.sub.5, and mixtures thereof.
8. (canceled)
9. The electrode active material of claim 1 wherein the
silver-containing material is AgVO.sub.3 and the silver vanadium
oxide has a BET surface area of about 15.2 m.sup.2/g.
10. A nonaqueous electrochemical cell, which comprises: a) an anode
comprising lithium; b) a cathode comprising silver vanadium oxide
characterized as having been prepared from a mixture of a
silver-containing material and a vanadium-containing material in a
solution contained in a closed vessel heated to a reaction
temperature above ambient of not greater than about 300.degree. C.
to produce the silver vanadium oxide having the formula
Ag.sub.2V.sub.4O.sub.11; c) a separator electrically isolating the
anode from the cathode, and of a porosity to allow for ion flow
there through; and d) a non-aqueous electrolyte activating the
anode and the cathode.
11. The electrochemical cell of claim 10 wherein the reaction
temperature inside the closed vessel is about 120.degree. C. to
about 300.degree. C.
12. The electrochemical cell of claim 10 wherein the pressure in
the closed vessel at the reaction temperature is about 14.7 psi to
about 1,800 psi.
13. The electrochemical cell of claim 10 wherein the solution
inside the closed vessel is characterized as having been heated at
the reaction temperature for about 1 hour to about 30 hours.
14. The electrochemical cell of claim 10 wherein the
.epsilon.-phase silver vanadium oxide is characterized as having
been cooled from the reaction temperature to ambient temperature in
the closed vessel.
15. The electrochemical cell of claim 10 wherein the silver- and
vanadium-containing materials are in a stoichiometric molar
proportion in an aqueous solution in the closed vessel to give a
Ag:V ratio of about 1:2.
16. The electrochemical cell of claim 10 wherein the
silver-containing material is selected from the group consisting of
elemental silver, silver oxide, silver carbonate, silver lactate,
silver triflate, silver pentafluoropropionate, silver laurate,
silver myristate, silver palmitate, silver stearate, silver
vanadate, and mixtures thereof, and wherein the vanadium-containing
material is selected from the group consisting of NH.sub.4VO.sub.3,
AgVO.sub.3, VO, VO.sub.1.27, VO.sub.2, V.sub.2O.sub.4,
V.sub.2O.sub.3, V.sub.3O.sub.5, V.sub.4O.sub.9, V.sub.6O.sub.13,
V.sub.2O.sub.5, and mixtures thereof.
17. A method for producing a cathode active material, comprising
the steps of: a) providing a silver-containing material; b)
providing a vanadium-containing material; c) mixing the silver- and
vanadium-containing materials together in an aqueous solution in a
closed vessel; and d) heating the solution to a reaction
temperature of not greater than about 300.degree. C. and a pressure
above ambient up to about 1,800 psi to produce an .epsilon.-phase
silver vanadium oxide having the formula
Ag.sub.2V.sub.4O.sub.11.
18. (canceled)
19. The method of claim 17 including heating the solution to the
reaction temperature in a range from about 120.degree. C. to about
300.degree. C.
20. The method of claim 17 including heating the solution at the
reaction temperature from about 1 hour to about 30 hours.
21. The method of claim 17 including cooling the .epsilon.-phase
silver vanadium oxide from the reaction temperature to ambient
temperature in the closed vessel.
22. The method of claim 17 including providing the silver- and
vanadium-containing materials in a stoichiometric molar proportion
in the solution in the closed vessel to give a Ag:V ratio of about
1:2.
23. The method of claim 17 including selecting the
silver-containing material from the group consisting of elemental
silver, silver oxide, silver carbonate, silver lactate, silver
triflate, silver pentafluoropropionate, silver laurate, silver
myristate, silver palmitate, silver stearate, silver vanadate, and
mixtures thereof, and including selecting the vanadium-containing
material from the group consisting of NH.sub.4VO.sub.3, AgVO.sub.3,
VO, VO.sub.1.27, VO.sub.2, V.sub.2O.sub.4, V.sub.2O.sub.3,
V.sub.3O.sub.5, V.sub.4O.sub.9, V.sub.6O.sub.13, V.sub.2O.sub.5,
and mixtures thereof.
24. The method of claim 17 wherein the silver-containing material
is Ag.sub.2O and the .epsilon.-phase silver vanadium oxide has a
BET surface area of about 26.9 m.sup.2/g.
25. The method of claim 17 wherein the silver-containing material
is AgVO.sub.3 and the .epsilon.-phase silver vanadium oxide has a
BET surface area of about 15.2 m.sup.2/g.
26. A method for producing a cathode active material, comprising
the steps of: a) providing a first metal-containing material; b)
providing a vanadium-containing material; c) mixing the first
metal- and vanadium-containing materials together in an aqueous
solution in a closed vessel; and d) heating the solution to a
reaction temperature of not greater than about 300.degree. C. and a
pressure above ambient up to about 1,800 psi to produce a
transition metal oxide.
27. (canceled)
28. The method of claim 26 including heating the aqueous solution
to the reaction temperature in a range from about 120.degree. C. to
about 300.degree. C.
29. The method of claim 26 including heating the aqueous solution
at the reaction temperature from about 1 hour to about 30
hours.
30. The method of claim 26 including cooling the transition metal
oxide from the reaction temperature to ambient temperature in the
closed vessel.
31. The method of claim 26 including providing the first metal
(FM)-containing material as a silver-containing material mixed with
the vanadium-containing material in a stoichiometric molar
proportion in the range of Ag:V of about 0.4:1.
32. The method of claim 26 including providing the first metal
(FM)-containing material as a silver-containing material mixed with
the vanadium-containing material in a stoichiometric molar
proportion in the range of Ag:V of about 0.16:1.
33. The method of claim 26 including providing the first metal
(FM)-containing material as a silver-containing material mixed with
the vanadium-containing material in a stoichiometric molar
proportion in the range of Ag:V of about 1:1.
34. The method of claim 26 including providing the first metal
(FM)-containing material as a copper-containing material mixed with
the vanadium-containing material in a stoichiometric molar
proportion in the range of Cu:V of about 0.01:1 to about 2:1.
35. The method of claim 26 including providing the first metal
(FM)-containing material as a copper-containing material and
further providing a second metal (SM)-containing material as a
silver-containing material mixed with the vanadium-containing
material in a stoichiometric molar proportion in the range of
Cu:Ag:V of about 0.01:0.01:1 to about 2:2:1.
36. The method of claim 26 including providing the first metal
(FM)-containing material as a manganese-containing material and
further providing a second metal (SM)-containing material as a
silver-containing material mixed with the vanadium-containing
material in a stoichiometric molar proportion in the range of
Mn:Ag:V of about 0.01:0.01:1 to about 2:2:1.
37. The method of claim 26 including providing the first metal
(FM)-containing material as a magnesium-containing material and
further providing a second metal (SM)-containing material as a
silver-containing material mixed with the vanadium-containing
material in a stoichiometric molar proportion in the range of
Mg:Ag:V of about 0.01:0.01:1 to about 2:2:1.
38. The method of claim 26 including selecting the
vanadium-containing material from the group consisting of
NH.sub.4VO.sub.3, AgVO.sub.3, VO, VO.sub.1.27, VO.sub.2,
V.sub.2O.sub.4, V.sub.2O.sub.3, V.sub.3O.sub.5, V.sub.4O.sub.9,
V.sub.6O.sub.13, V.sub.2O.sub.5, and mixtures thereof.
39. The method of claim 26 wherein the first metal-containing
material is selected from the group consisting of elemental silver,
silver oxide, silver carbonate, silver lactate, silver triflate,
silver pentafluoropropionate, silver laurate, silver myristate,
silver palmitate, silver stearate, silver vanadate, and mixtures
thereof, and the transition metal oxide is silver vanadium
oxide.
40. The method of claim 26 wherein the first metal-containing
material is either copper oxide or copper carbonate and the
transition metal oxide is manganese silver vanadium oxide
41. The method of claim 26 wherein the first metal-containing
material is either manganese oxide or manganese carbonate and the
transition metal oxide is manganese silver vanadium oxide.
42. The method of claim 26 wherein the first metal-containing
material is either magnesium oxide or magnesium carbonate and the
transition metal oxide is magnesium silver vanadium oxide.
43. The method of claim 26 wherein the cathode active material is
silver vanadium oxide having a primary particle diameter of about
27 nm to about 33 nm.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority from provisional
application Ser. No. 60/488,271, filed Jul. 18, 2003.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention generally relates to the conversion of
chemical energy to electrical energy. More particularly, the
present invention relates to the preparation of an improved
transition metal oxide cathode active material for non-aqueous
lithium electrochemical cells prepared by a hydrothermal reaction.
A most preferred cathode active material is .epsilon.-phase silver
vanadium oxide (SVO, Ag.sub.2V.sub.4O.sub.11). Silver vanadium
oxide prepared by a hydrothermal synthesis is unlike
.epsilon.-phase SVO prepared by prior art methods using solid-state
thermal reactions or sol-gel techniques, and is particularly useful
in an implantable electrochemical cell, for example of the type
powering a cardiac defibrillator. In this type of application, the
cell may run under a light load for significant periods interrupted
from time to time by high rate pulse discharges, which
.epsilon.-phase silver vanadium oxide is uniquely suited for.
[0004] 2. Prior Art
[0005] Thermal synthesis of silver vanadium oxide can be
accomplished by chemical decomposition, combination, or both
decomposition and combination reactions. Synthesis of SVO by
heating to induce a decomposition of the reactants is detailed in
U.S. Pat. Nos. 4,310,609 and 4,391,729, both to Liang et al. This
technique is further discussed in the publication: Leising, R. A.;
Takeuchi, E. S. Chem. Mater. 1993, 5, 738-742. A typical example of
a decomposition reaction resulting in the formation of SVO involves
heat treatment of a mixture of AgNO.sub.3 and V.sub.2O.sub.5 to a
final temperature of from about 350.degree. C. to about 520.degree.
C. The combination of Ag.sub.2O and V.sub.2O.sub.5 heated to a
maximum temperature of 520.degree. C. to form SVO is described by
Crespi in U.S. Pat. No. 5,221,453, and the synthesis of SVO at
500.degree. C. via a dual decomposition/combination reaction is
described in the publication: Leising, R. A.; Takeuchi, E. S. Chem.
Mater. 1994, 6, 489-495. All of these SVO synthesis procedures
share a high temperature thermal treatment step as a common
process.
[0006] Silver vanadium oxide has also been synthesized via sol-gel
methods. U.S. Pat. No. 5,558,680 to Takeuchi et al. describes the
preparation of SVO utilizing sol-gel synthesis, with a final
heating step of about 375.degree. C. to about 450.degree. C. Thus,
although sol-gel technology is typically used for the preparation
of materials at relatively low-temperatures, the synthesis of SVO
by sol-gel techniques in the prior art has been limited to high
temperature thermal treatments.
[0007] Hydrothermal synthesis has been used to prepare compounds
other than SVO. For example, Myung, S.-T.; Komaba, S.; Kumagai, N.
J. Electrochem. Soc. 149, A1349-A1357 (2002) describe the
"Hydrothermal Synthesis of Orthorhombic LiCo.sub.xMn.sub.1-xO.sub.2
and Their Structural Changes During Cycling." Furthermore, Nitta,
Y.; Nagayama, M.; Miyahe, H.; Ohta, A. J. of Power Sources 81-82,
49-53 (1999) detail the "Synthesis and reaction mechanism of 3 V
LiMnO.sub.2". While these disparate materials have been synthesized
for use as battery cathode materials, the prior art hydrothermal
reactions do not include transition metal oxides, such as SVO, as a
contemplated cathode material. Furthermore, low temperature
synthesis of SVO, regardless the preparation technique, has not
been explored. Therefore, the preparation of transition metal
oxides including SVO via hydrothermal synthesis at a relatively low
temperature is a new discovery with unexpected results.
[0008] The above prior art patents and publications are
incorporated herein by reference.
SUMMARY OF THE INVENTION
[0009] The current invention relates to the preparation of an
improved cathode active material for non-aqueous lithium
electrochemical cells, and in particular, a cathode active material
containing a transition metal oxide, preferably .epsilon.-phase
SVO, prepared using a hydrothermal synthesis. For silver vanadium
oxide, the hydrothermal reaction involves mixing a
silver-containing material, such as a silver salt, with a
vanadium-containing material in an aqueous solution heated at a
relatively low temperature inside a pressure vessel. The preferred
product .epsilon.-phase SVO possesses a higher surface area than
.epsilon.-phase SVO produced by other synthesis techniques, such as
by decomposition, addition or sol-gel reactions. The relatively
high surface area of the product .epsilon.-phase SVO is a result of
the low temperature used in the preparation of the material. For
this reason, the .epsilon.-phase SVO exhibits greater long-term
stability when used as a cathode active material in comparison to
SVO with a lower specific surface area.
[0010] In addition, the high surface area SVO is a pure
.epsilon.-phase material. By comparison, prior art thermal
treatment and sol-gel synthesis techniques require high temperature
steps to achieve phase pure SVO materials. However, the use of high
temperature steps results in significant material sintering,
resulting in a relatively low surface area product.
[0011] The present synthesis technique is not, however, limited to
SVO. Salts of copper, magnesium and manganese can be used to
produce alternate relatively high surface area transition metal
oxide electrode active materials by hydrothermal synthesis as
well.
[0012] These and other objects of the present invention will become
increasingly more apparent to those skilled in the art by a reading
of the following detailed description in conjunction with the
appended drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a SEM micrograph of SVO prepared by the
hydrothermal synthesis described in Example II.
[0014] FIG. 2 is a SEM micrograph of SVO prepared by the prior art
decomposition reaction described in Comparative Example III.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0015] As used herein, the term "low temperature synthesis" means
an aqueous solution containing two or more starting constituents
heated to a maximum reaction temperature, no matter how many
heating events there are, that is not greater than about
300.degree. C.
[0016] The present invention describes a hydrothermal synthesis for
preparing cathode materials for use in lithium electrochemical
cells. In the hydrothermal synthesis of silver vanadium oxide
having the general formula of Ag.sub.xV.sub.2O.sub.y, the silver-
and vanadium-containing reactants are combined in stoichiometric
molar proportions to give a Ag:V ratio of 1:2 for Ag.sub.2 and
V.sub.2O.sub.5 starting materials for the .epsilon.-phase
(Ag.sub.2V.sub.4O.sub.11). For the silver vanadate (AgVO.sub.3)
combined with V.sub.2O.sub.5, the molar proportion of Ag:V is 1:1.
Hydrothermal synthesis is also useful for producing .beta.-phase
SVO having in the general formula x=0.33 and y=5 with a Ag:V molar
ratio is about 0.16:1, and .gamma.-phase SVO having x=0.74 and
y=5.37 with the Ag:V molar ratio is about 0.4:1, or a mixture of
the phases thereof.
[0017] Suitable silver-containing materials include elemental
silver (Ag, T.sub.m 962.degree. C.), silver oxide (Ag.sub.2O,
T.sub.m 230.degree. C.), silver carbonate (Ag.sub.2CO.sub.3),
T.sub.m 210.degree. C.), silver lactate (AgC.sub.3H.sub.5O.sub.3,
T.sub.m 120.degree. C.), silver triflate (AgCF.sub.3SO.sub.3,
T.sub.m 286.degree. C.), silver pentafluoropropionate
(AgC.sub.3F.sub.5O.sub.2, T.sub.m 242.degree. C.), silver laurate
(AgC.sub.12H.sub.23O.sub.2, T.sub.m 212.degree. C.), silver
myristate (AgC.sub.14H.sub.27O.sub.2, T.sub.m 211.degree. C.)
silver palmitate (AgC.sub.16H.sub.31O.sub.2, T.sub.m 209.degree.
C.), silver stearate (AgC.sub.18H.sub.35O.sub.2, T.sub.m
205.degree. C.), silver vanadate (AgVO.sub.3, T.sub.m 465.degree.
C.), and mixtures thereof. Suitable vanadium-containing materials
include NH.sub.4VO.sub.3, AgVO.sub.3, VO, VO.sub.1.27, VO.sub.2,
V.sub.2O.sub.4, V.sub.2O.sub.3, V.sub.3O.sub.5, V.sub.4O.sub.9,
V.sub.6O.sub.13, V.sub.2O.sub.5, and mixtures thereof.
[0018] A typical hydrothermal reaction mechanism is illustrated in
equation 1 for .epsilon.-phase silver vanadium oxide:
Ag.sub.2O+2V.sub.2O.sub.5.fwdarw.Ag.sub.2V.sub.4O.sub.11 (1)
[0019] Regardless the reactants, they are first ground, then added
to an aqueous solution in a pressurized vessel and heated to a
temperature of about 120.degree. C. to about 300.degree. C. for
about 1 to 30 hours. Longer heating times are required for lower
heating temperatures. The heating in the vessel is at a pressure
range of about 14.7 psi to a maximum of about 1,800 psi. In that
respect, the maximum heating temperature inside the pressure vessel
can be either above or below the melting point of the reactive
constituents. More important is that the heating takes place in an
aqueous solution at a pressure above ambient.
[0020] When silver oxide (Ag.sub.2O) and vanadium pentoxide
(V.sub.2O.sub.5) are used in the synthesis, their homogeneous
mixture in an aqueous solution contained inside a pressurized
vessel is preferably heated to about 240.degree. C. for at least
about 12 hours. This temperature range is much lower than the
typical solid-state thermal synthesis temperatures of about
500.degree. C. to 1,000.degree. C.
[0021] The following examples describe the manner and process of
the present invention, and they set forth the best mode
contemplated by the inventors of carrying out the invention, but
they are not to be construed as limiting.
Example I
[0022] Silver vanadium oxide was synthesized under hydrothermal
conditions using Ag.sub.2O and V.sub.2O.sub.5 in a molar ratio of
1:2. In particular, 0.116 grams of Ag.sub.2O was added to 0.182
grams of V.sub.2O.sub.5 and the solids were ground together with a
mortar and pestle to pass the entire mixture through a 230-mesh
sieve. The solids were combined with 9 ml of distilled/de-ionized
water and placed in a Model 4744 Acid Digestion Bomb (Parr Inst.).
The sealed vessel was heated to about 240.degree. C. over a period
of about 2.5 hours, held at about 240.degree. C. for about 12
hours, and then slowly cooled to room temperature over a period of
about 8 hours. The SVO product was separated from the water
solution, dried at about 120.degree. C. for about 16 hours, and
ground with a mortar and pestle.
Example II
[0023] Silver vanadium oxide was synthesized under hydrothermal
conditions using AgVO.sub.3 and V.sub.2O.sub.5 in a molar ratio of
2:1. In particular, 0.414 grams of AgVO.sub.3 was added to 0.182
grams of V.sub.2O.sub.5 and the solids were ground together with a
mortar and pestle to pass the entire mixture through a 120-mesh
sieve. The solids were combined with 9 ml of distilled/de-ionized
water and placed in the Model 4744 Acid Digestion Bomb. The sealed
vessel was heated to about 240.degree. C. over a period of about
2.5 hours, held at about 240.degree. C. for about 12 hours, and
then slowly cooled to room temperature over a period of about 8
hours. The SVO product was separated from the water solution, dried
at about 110.degree. C. for about 16 hours under vacuum, and ground
with a mortar and pestle.
Comparative Example I
[0024] Silver vanadium oxide was synthesized by the prior art high
temperature thermal treatment method using Ag.sub.2O and
V.sub.2O.sub.5 in a 1:2 molar ratio. In particular, 102.46 grams of
Ag.sub.2O was added to 160.84 grams of V.sub.2O.sub.5 and the
solids were mixed together with a blender. The mixture was heated
to about 500.degree. C. in a furnace under an air atmosphere for
about 50 hours of total heating time. During the high
temperature-heating step, the sample was cooled to room
temperature, ground with mortar and pestle and re-heated to about
500.degree. C. The resulting material was used as synthesized.
Comparative Example II
[0025] Silver vanadium oxide was synthesized by the prior art high
temperature thermal treatment method using AgVO.sub.3 and
V.sub.2O.sub.5 in a 2:1 molar ratio. In particular, 182.89 grams of
AgVO.sub.3 was added to 80.43 grams of V.sub.2O.sub.5 and the
solids were mixed together with a blender. The mixture was heated
to about 500.degree. C. in a furnace under an air atmosphere for
about 50 hours of total heating time. During the high temperature
heating step, the sample was cooled to room temperature, ground
with mortar and pestle and re-heated to about 500.degree. C. The
resulting material was used as synthesized.
Comparative Example III
[0026] Silver vanadium oxide was synthesized by the prior art high
temperature thermal treatment method using AgNO.sub.3 and
V.sub.2O.sub.5 in a 1:1 molar ratio. In particular, 1.826 grams of
AgNO.sub.3 was added to 1.938 grams of V.sub.2O.sub.5 and the
solids were ground together with a mortar and pestle to pass the
entire mixture through a 120-mesh sieve. The mixture was added to a
porcelain boat, and heated to about 300.degree. C. in a tube
furnace under flowing air for about 16 hours. The sample was cooled
to room temperature, ground with mortar and pestle and heated to
about 500.degree. C. for about 16 hours. The resulting material was
used as synthesized.
Comparative Example IV
[0027] Silver vanadium oxide was synthesized via the prior art
sol-gel method described in the previously discussed U.S. Pat. No.
5,558,680 to Takeuchi et al. using LiOH, AgNO.sub.3 and
V.sub.2O.sub.5, in a molar ratio of 0.05:0.95:2.0. In particular,
23.03 grams of V.sub.2O.sub.5 was mixed with 10.23 grams of
AgNO.sub.3 and 0.0075 grams of LiOH to give 33.33 grams of total
solids. The mixture was added to 100 ml of distilled water to form
a slurry that was about 25% solids and/or dissolved solids per
solution weight. The slurry was heated to about 90.degree. C. for
about 3 hours with stirring. The sample was then cooled prior to
dehydration and sintering at about 375.degree. C. for about 24
hours under ambient atmosphere.
[0028] The XRD powder patterns collected for both the hydrothermal
SVO and the prior art SVO materials demonstrate that the materials
are all of a .epsilon.-phase (Ag.sub.2V.sub.4O.sub.11). However,
the hydrothermal synthesis of SVO described herein produces an
active material that is different in surface area and morphology
from that produced by the previously described prior art solid
state thermal synthesis (Comparative Example I, II and III) and
sol-gel technique (Comparative Example IV).
[0029] The SEM analysis of the competing products shows that the
primary particle size of the hydrothermal SVO is significantly
smaller than the primary particle size of the prior art SVO. This
is illustrated in FIGS. 1 and 2. FIG. 1 is a SEM micrograph
(magnification=10,000.times., system vacuum=1.32e-006 Torr,
EHT=10.00 kv, WD=6 mm and signal A+SE1) of SVO prepared under
hydrothermal conditions according to Example II. FIG. 2 is a SEM
micrograph (magnification=10,000.times., system vacuum=7.58e-007
Torr, EHT=10.00 kv, WD=5 mm and signal A+SE1) of SVO prepared by
the prior art thermal treatment method according to Comparative
Example III.
[0030] In addition, the BET surface areas of the SVO materials are
quite different, as illustrated in Table 1.
TABLE-US-00001 TABLE 1 Synthesis Final BET Example Technique
Temperature Surf. Area I Hydrothermal 240.degree. C. 26.9 m.sup.2/g
II Hydrothermal 240.degree. C. 15.2 m.sup.2/g Comp. I High Temp
Thermal 500.degree. C. 0.7 m.sup.2/g Comp. II High Temp Thermal
500.degree. C. 0.6 m.sup.2/g Comp. III High Temp Thermal
500.degree. C. 0.4 m.sup.2/g Comp. IV Sol-Gel 375.degree. C. 8.2
m.sup.2/g
[0031] The SVO synthesized by hydrothermal reactions yielded much
higher BET surface areas, consistent with the small primary
particle size of this material. The small particle size and high
surface area of the hydrothermal SVO makes this unique material
ideal for use as a cathode in high rate discharge applications.
[0032] Additionally, the SVO particles are of a nano particle size.
For Example I, the primary particle diameter was measured as low as
27 nm in a 30,000.times.SEM image. For Example II, the primary
particle diameter was measured as low as 33 nm in a
30,000.times.SEM image.
[0033] The above detailed description and examples are intended for
the purpose of illustrating the invention, and are not to be
construed as limiting. For example, the following compounds are
reacted with any one of the above listed vanadium oxides as a
homogeneous mixture in an aqueous solution contained inside a
pressurized vessel heated to a temperature of about 120.degree. C.
to about 300.degree. C. for about 1 to 30 hours to form alternate
cathode active materials. For the production of copper silver
vanadium oxide, CSVO, (Cu.sub.0.2Ag.sub.0.8V.sub.2O.sub.5.6), they
are copper oxide (CuO, T.sub.m 1,446.degree. C.) or copper
carbonate (Cu.sub.2Co.sub.3). The preferred molar proportion of
Cu:Ag:V is in the range of 0.01:0.01:1 to 2:2:1.
[0034] For the production of copper vanadium oxide, CVO,
(CuV.sub.2O.sub.6), they are copper oxide (CuO, T.sub.m
1,446.degree. C.) or copper carbonate (Cu.sub.2Co.sub.3). The
preferred molar proportion of Cu:V is in the range of 0.01:1 to
2:1
[0035] For the production of manganese silver vanadium oxide,
MnSVO, (Mn.sub.0.2Ag.sub.0.8V.sub.2O.sub.5.8), manganese carbonate
(MnCO.sub.3) or manganese oxide (MnO, T.sub.m 1,650.degree. C.) are
used. The preferred molar proportion of MN:Ag:V is in the range of
0.01:0.01:1 to 2:2:1.
[0036] For the production of magnesium silver vanadium oxide,
MgSVO, (Mg.sub.0.2Ag.sub.0.8V.sub.2O.sub.5.6), magnesium carbonate
(MgCO.sub.3, T.sub.d 350.degree. C.) or magnesium oxide (MgO,
T.sub.m 2,826.degree. C.) are suitable. The preferred molar
proportion of Mg:Ag:V is in the range of 0.01:0.01:1 to 2:2:1.
[0037] The use of the above mixed metal oxides as a cathode active
material provides an electrochemical cell that possesses sufficient
energy density and discharge capacity required for the vigorous
requirements of implantable medical devices. These types of cells
comprise an anode of a metal selected from Groups IA, IIA and IIIB
of the Periodic Table of the Elements. Such anode active materials
include lithium, sodium, potassium, etc., and their alloys and
intermetallic compounds including, for example, Li--Mg, Li--Si,
Li--Al, Li--B and Li--Si--B alloys and intermetallic compounds. The
preferred anode comprises lithium. An alternate anode comprises a
lithium alloy such as a lithium-aluminum alloy. The greater the
amounts of aluminum present by weight in the alloy, however, the
lower the energy density of the cell.
[0038] The form of the anode may vary, but preferably it is a thin
metal sheet or foil of the anode metal, pressed or rolled on a
metallic anode current collector, i.e., preferably comprising
titanium, titanium alloy or nickel, to form an anode component.
Copper, tungsten and tantalum are also suitable materials for the
anode current collector. In the exemplary cell of the present
invention, the anode current collector has an extended tab or lead,
i.e., preferably of nickel or titanium, contacted by a weld to a
cell case of conductive metal in a case-negative electrical
configuration. Alternatively, the anode may be formed in some other
geometry, such as a bobbin shape, cylinder or pellet to allow an
alternate low surface cell design.
[0039] Before the previously described .epsilon.-phase SVO or
alternate cathode active materials are fabrication into a cathode
electrode for incorporation into an electrochemical cell, they are
preferably mixed with a binder material, such as a powdered
fluoro-polymer, more preferably powdered polytetrafluoroethylene
(PTFE) or powdered polyvinylidene fluoride (PVDF), present at about
1 to about 5 weight percent of the cathode mixture. Further, up to
about 10 weight percent of a conductive diluent is preferably added
to the cathode mixture to improve conductivity. Suitable materials
for this purpose include acetylene black, carbon black and/or
graphite or a metallic powder such as of nickel, aluminum, titanium
and stainless steel. The preferred cathode active mixture thus
includes a powdered fluoro-polymer binder present at about 3 weight
percent, a conductive diluent present at about 3 weight percent and
about 94 weight percent of the cathode active material. For
example, depending on the application of the electrochemical cell,
the range of cathode compositions is from about 99% to about 80%,
by weight, .epsilon.-phase silver vanadium oxide mixed with carbon
graphite and PTFE.
[0040] Cathode components for incorporation into an electrochemical
cell according to the present invention may be prepared by rolling,
spreading or pressing the cathode active materials onto a suitable
current collector selected from stainless steel, titanium,
tantalum, platinum, gold, aluminum, cobalt-nickel alloys,
nickel-containing alloys, highly alloyed ferritic stainless steel
containing molybdenum and chromium, and nickel-, chromium- and
molybdenum-containing alloys. Cathodes prepared as described above
may be in the form of one or more plates operatively associated
with at least one or more plates of anode material, or in the form
of a strip wound with a corresponding strip of anode material in a
structure similar to a "jellyroll".
[0041] In order to prevent internal short circuit conditions, the
cathode is separated from the Group IA, IIA or IIIB anode by a
suitable separator material. The separator is of electrically
insulative material, and the separator material also is chemically
unreactive with the anode and cathode active materials and both
chemically unreactive with and insoluble in the electrolyte. In
addition, the separator material has a degree of porosity
sufficient to allow flow there through of the electrolyte during
the electrochemical reaction of the cell. Illustrative separator
materials include fabrics woven from fluoropolymeric fibers
including polyvinylidine fluoride, polyethylenetetrafluoroethylene,
and polyethylenechlorotrifluoroethylene used either alone or
laminated with a fluoropolymeric microporous film, non-woven glass,
polypropylene, polyethylene, glass fiber materials, ceramics, a
polytetrafluoroethylene membrane commercially available under the
designation ZITEX (Chemplast Inc.), a polypropylene membrane
commercially available under the designation CELGARD (Celanese
Plastic Company, Inc.) and a membrane commercially available under
the designation DEXIGLAS (C.H. Dexter, Div., Dexter Corp.).
[0042] The electrochemical cell further includes a nonaqueous,
ionically conductive electrolyte that serves as a medium for
migration of ions between the anode and the cathode electrodes
during the electrochemical reactions of the cell. The
electrochemical reaction at the electrodes involves conversion of
ions in atomic or molecular forms that migrate from the anode to
the cathode. Thus, suitable nonaqueous electrolytes are
substantially inert to the anode and cathode materials, and they
comprise an inorganic, ionically conductive salt dissolved in a
nonaqueous solvent. More preferably, the electrolyte includes an
ionizable alkali metal salt dissolved in a mixture of aprotic
organic solvents comprising a low viscosity solvent and a high
permittivity solvent. The salt serves as the vehicle for migration
of the anode ions to intercalate or react with the cathode active
material. Preferably, the salt is lithium based including
LiPF.sub.6, LiBF.sub.4, LiAsF.sub.6, LiSbF.sub.6, LiClO.sub.4,
LiO.sub.2, LiAlCl.sub.4, LiGaCl.sub.4, LiC(SO.sub.2CF.sub.3).sub.3,
LiN(SO.sub.2CF.sub.3).sub.2, LiSCN, LiO.sub.3SCF.sub.3,
LiC.sub.6F.sub.5SO.sub.3, LiO.sub.2CCF.sub.3, LiSO.sub.6F,
LiB(C.sub.6H.sub.5).sub.4, LiCF.sub.3SO.sub.3, and mixtures
thereof.
[0043] Low viscosity solvents useful with the present invention
include esters, linear and cyclic ethers and dialkyl carbonates
such as tetrahydrofuran (THF), methyl acetate (MA), diglyme,
trigylme, tetragylme, dimethyl carbonate (DMC), 1,2-dimethoxyethane
(DME), 1,2-diethoxyethane (DEE), 1-ethoxy,2-methoxyethane (EME),
ethyl methyl carbonate, methyl propyl carbonate, ethyl propyl
carbonate, diethyl carbonate, dipropyl carbonate, and mixtures
thereof. Suitable high permittivity solvents include cyclic
carbonates, cyclic esters and cyclic amides such as propylene
carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC),
acetonitrile, dimethyl sulfoxide, dimethyl formamide, dimethyl
acetamide, .gamma.-valerolactone, .gamma.-butyrolactone (GBL),
N-methyl-pyrrolidinone (NMP), and mixtures thereof. The preferred
electrolyte for a Li/SVO cell is 0.8M to 1.5M LiAsF.sub.6 or
LiPF.sub.6 dissolved in a 50:50 mixture, by volume, of propylene
carbonate and 1,2-dimethoxyethane.
[0044] The preferred form of a primary alkali metal/solid cathode
electrochemical cell is a case-negative design. This is where the
anode is in contact with a conductive metal casing and the cathode
contacted to a current collector is the positive terminal. The
cathode current collector is in contact with a positive terminal
pin via a lead welded to both the current collector and the
positive terminal pin.
[0045] A preferred material for the casing is titanium although
stainless steel, mild steel, nickel-plated mild steel and aluminum
are also suitable. The casing header comprises a metallic lid
having an opening to accommodate the glass-to-metal seal/terminal
pin feedthrough for the cathode electrode. The anode electrode is
preferably connected to the case or the lid. An additional opening
is provided for electrolyte filling. The casing header is corrosion
resistant and is compatible with the other components of the
electrochemical cell. The cell is thereafter filled with the
electrolyte solution described hereinabove and hermetically sealed
such as by close-welding a titanium plug over the fill hole, but
not limited thereto. The cell of the present invention can also be
constructed in a case-positive design, as is well known by those
skilled in the art.
[0046] It is appreciated that various modifications to the
inventive concepts described herein may be apparent to those of
ordinary skill in the art without departing from the spirit and
scope of the present invention as defined by the appended
claims.
* * * * *